Efficient Photoluminescent Materials with Flexible Electronics, Their Preparation Methods and Applications

Abstract

The present invention belongs to the field of metal-organic framework materials, and particularly relates to a highly efficient photoluminescent material with flexible electronics, its preparation method and application. The molecular formula of the single crystal structure of the complex material is: [Zn(μ-L)(μ-bix)] n ·0.33nH2O; where H2L is biphenyl-3,5-dicarboxylic acid; bix is 1,4-bis[(1H-imidazol-1-yl)methyl]benzene. The complex material MOF-NT of the present invention follows the anti-Kasha rule, has high fluorescence emission efficiency and photoluminescence quantum yield, and can be used as a highly sensitive fluorescence probe to distinguish and detect volatile organic compounds by fluorescence resonance energy transfer, showing a discriminatory PL response between isomers of nitroaromatic compounds. The present invention demonstrates that the fluorescence emission of the anti-Kasha rule can be achieved in crystalline MOF materials, providing a new direction for the development of advanced solid-state fluorescence emission materials. In addition, the low detection limit of MOF-NT for acetone also makes it have the potential to be used as a sensor in the fields of toxicology and physiology.

Description

Technical Field

[0001] The present invention belongs to the field of metal-organic framework materials, and particularly relates to a highly efficient photoluminescent material with flexible electronics, a preparation method thereof, and an application thereof. Background Art

[0002] Metal-organic frameworks (MOFs) are a class of emerging highly crystalline porous materials with a wide range of applications, including gas storage and separation, sensing, and catalysis.

[0003] Flexible electronics refers to the fact that the framework between different electronic structures can undergo reversible changes under the action of various external chemical and physical stimuli (such as light, temperature, pressure, or chemical substances). This may lead to color change, photoluminescence, magnetic transition, and other unique functional responses. In the field of MOFs, flexible structures have been widely explored, while flexible electronics has hardly been involved in the research field.

[0004] Fluorescent MOFs are a kind of crystalline materials with strong fluorescence and high-order porosity, and have broad application prospects in the fields of biological imaging, lighting, and display technology. Generally, the fluorescence emission of MOFs follows the Kasha's rule, that is, it is independent of the excitation energy, because before fluorescence emission, all high-energy excitons will relax to the lowest excited state through internal conversion (IC). Therefore, the abnormal phenomenon of excitation-dependent fluorescence (EDF) can be observed in carbon nanostructures, including graphene quantum dots (GQDs) and other graphene oxide derivatives (GODs). By changing the excitation wavelength, its emission color can be easily adjusted. However, the EDF fluorescence of most carbon nanomaterials involves the participation of polar solvents; its EDF mechanism has also been controversial for a long time. Compared with carbon-based nanomaterials, MOF-based materials hardly show EDF fluorescence, especially crystalline MOFs with controllable emission wavelengths. It has the following advantages: it can be directly used without being dissolved in a solvent; it can be used for on-line detection and analysis; it has good reusability, etc.

[0005] Therefore, it is very necessary to develop a new type of MOF material with flexible electronics. Summary of the Invention

[0006] The present invention provides a highly efficient photoluminescent material with flexible electronics, a preparation method thereof, and an application thereof. The first object is to develop a new type of MOF material with flexible electronics, specifically a multifunctional fluorescent material with highly efficient photoluminescence with flexible electronics (hereinafter simply referred to as MOF-NT). MOF-NT is assembled from two different emissive linkers: biphenyl-3,5-dicarboxylic acid (H2L) and 1,4-bis[(1H-imidazol-1-yl)methyl]benzene (bix).

[0007] The above technical object of the present invention is achieved by the following technical solutions:

[0008] In the first aspect of the present invention, a highly efficient photoluminescent material with flexible electronics is provided. The single crystal structure molecular formula of the material is: [Zn(μ-L)(μ-bix)] n ·0.33nH2O; wherein, H2L is biphenyl-3,5-dicarboxylic acid, and bix is 1,4-bis[(1H-imidazol-1-yl)methyl]benzene.

[0009] Furthermore, the emission peak position of the material shifts by at least 170 nm. The fluorescence emission of the MOF-NT crystal solid follows the anti-Kasha rule, has a high fluorescence emission efficiency, and exhibits excitation-dependent fluorescence extending from the ultraviolet to the visible spectral region. Therefore, the emission offset of the material is at least 170 nm.

[0010] Furthermore, at the optimal excitation wavelength, the photoluminescence quantum yield of the material at room temperature can reach up to 36.7%. Due to the multifunctional resonance structure of the imidazole-based ligand, at the optimal excitation wavelength, the photoluminescence quantum yield (PLQY) at room temperature can reach up to 36.7%.

[0011] In the second aspect of the present invention, a preparation method of a highly efficient photoluminescent material with flexible electronics is provided. The method includes: S1. Preparation of the organic ligand H2L: Place 5-bromo-m-xylene and phenylboronic acid in a reaction vessel, and at the same time add potassium carbonate dissolved in a mixed solvent of ethanol, toluene, and water to the reaction vessel and deoxygenate it under N2 to obtain a reaction mixture; Stir and add Pd(PPh3)4 to the reaction mixture, and reflux for 22 h to 26 h under N2; Evaporate to dryness under vacuum, extract with CH2Cl2, and then dry with MgSO4; Using n-hexane as the eluent, obtain a colorless liquid by silica gel chromatography; Add KMnO4 in four portions to the suspension of the colorless liquid containing water and pyridine, and reflux for three days; After cooling to room temperature, filter, then rinse repeatedly with water, and then adjust the pH value to 2 with hydrochloric acid and dry to obtain the organic ligand H2L; S2. Preparation of the organic ligand bix: Carry out reflux heating treatment on a methanol solution containing imidazole and α,α'-dichloro-p-xylene; Dissolve the yellow viscous liquid after evaporating methanol in an aqueous potassium carbonate solution; After standing, bix crystals are generated in the solution; And recrystallize from the solution to obtain the organic ligand bix; S3. Preparation of [Zn(μ-L)(μ-bix)] n ·0.33nH2O: Place the H2O / CH3CN mixed solvent of the mixture containing the organic ligand H2L, the organic ligand bix, and Zn(OAc)2·2H2O in a stainless steel high-pressure vessel; Stir and heat the mixture, and then cool to room temperature overnight to obtain the needle-shaped crystal [Zn(μ-L)(μ-bix)]n · 0.33 nH₂O. The synthesis raw materials for this preparation method are easily available, the synthesis method is simple, the yield is high, and it has the same technical effects.

[0012] Further, in the step S1, the molar ratio of 5-bromo-m-xylene, phenylboronic acid, and potassium carbonate is (38.75 - 38.95):(46.55 - 46.75):(89.93 - 90.33); the molar ratio of Pd(PPh₃)₄ and potassium permanganate is (0.87 - 1.07):(227.82 - 228.42); the volume ratio of ethanol, toluene, and water in the mixed solvent is (0.9 - 1.1):(1.9 - 2.1):(0.9 - 1.1); the volume ratio of water and pyridine in the suspension is (1.9 - 2.1):(0.9 - 1.1).

[0013] Further, in the step S2, the molar ratio of imidazole and α,α'-dichloro-p-xylene is (46.2 - 46.6):(4.36 - 4.56); the volume ratio of methanol and aqueous potassium carbonate solution is (0.9 - 1.1):(1.9 - 2.1).

[0014] Further, in the step S3, the molar ratio of the organic ligand H₂L, the organic ligand bix, and Zn(OAc)₂·2H₂O is (1.9 - 2.1):(1.9 - 2.1):(2.9 - 3.1); the volume ratio of H₂O to CH₃CN in the H₂O / CH₃CN mixed solvent is (1.8 - 2.2):(0.9 - 1.1).

[0015] Further, in the step S2, the time for the reflux heating treatment is 17 h to 19 h; in the step S3, the reaction temperature for heating the mixture after stirring is 165 °C to 175 °C, and the reaction time is (2.9 - 3.1) days.

[0016] The third aspect of the present invention provides the application of the above-mentioned high-efficiency photoluminescent material with flexible electronics as a fluorescent probe in the field of monitoring nitro explosives. MOF-NT utilizes the combined characteristics of multi-component PL and ordered porosity and can be used as a highly sensitive fluorescent probe to distinguish and detect volatile organic compounds, showing a discriminatory PL response between isomers of nitroaromatic compounds; this makes it have application prospects in selectively monitoring specific types of nitro explosives.

[0017] The fourth aspect of the present invention provides the application of the above-mentioned high-efficiency photoluminescent material with flexible electronics as a sensor in the fields of toxicology and physiology. The low detection limit of MOF-NT for acetone also makes it have the potential to be used as a sensor in the fields of toxicology and physiology.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The MOF-NT provided by the present invention is a multi-component MOF that follows the anti-Kasha emission rule, and the emission peak position of its fluorophore is related to the excitation wavelength. The present invention proves that the fluorescence emission of the anti-Kasha rule can be realized in the crystalline MOF material, providing ideas for the development of advanced solid-state emission materials.

[0020] (2) The MOF-NT provided by the present invention is representative of strong excitation-dependent fluorescence from the ultraviolet to the visible light region; the emission offset is at least 170 nm; it can be used as a highly sensitive fluorescence probe to distinguish and detect volatile organic compounds through fluorescence resonance energy transfer; it shows a discriminatory PL response between isomers of nitroaromatic compounds (NACs), and thus can be used for discriminative detection of NACs, which makes it have application prospects in selectively monitoring specific types of nitro explosives.

[0021] (3) The low detection limit and water solubility of acetone of the MOF-NT provided by the present invention make it have broad prospects in sensing applications in the fields of toxicology and physiology. Acetone is a highly volatile organic compound (VOC), and its toxicity can cause human metabolic disorders. The analysis of the acetone concentration in the body can provide important information for the diagnosis of certain diseases (such as diabetes). The general level of ketone bodies is usually lower than 0.5 mM, and values higher than 1.0 and 3.0 mM are considered hyperketonemia and ketoacidosis, respectively. Therefore, it is crucial to study an effective method for detecting trace ketone bodies in physiological samples.

[0022] (4) The highest value of the tunable PL quantum yield (PLQY) of the MOF-NT provided by the present invention at room temperature is unexpectedly as high as 36.7%. In pure carbon nanostructures (such as graphene quantum dots and other graphene oxide derivatives), the PLQY is usually lower than 15%, and its mechanism is related to the size effect and defect structure. For the photoluminescence mechanism of MOF-NT, its abnormal photoluminescence properties are related to the multifunctional resonance structure of imidazole-based ligands. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0024] Figure 1 It is a structural formula diagram of the high-efficiency photoluminescent material with flexible electronics provided by the present invention;

[0025] Figure 2 Synthesis method diagram of the organic ligand H2L in the present invention;

[0026] Figure 3 Synthesis method diagram of the organic ligand bix in the invention;

[0027] Figure 4 Fluorescence diagrams of Kasha's rule and anti-Kasha's rule;

[0028] Figure 5 Structure diagram of MOF-NT; Figure 6 Photoluminescence data of crystalline MOF-NT;

[0029] Figure 7 Diagram of the quenching rate (%) of MOF-NT emulsion in CH3OH and the PL spectrum of MOF-NT in the presence of different organic solvents after adding different volatile organic compounds (3%);

[0030] Figure 8 Normalized PL spectrum of MOF-NT emulsion in methanol with gradually increasing NACs concentration, λ ex = 290 nm;

[0031] Figure 9 Thermogravimetric diagram of MOF-NT in a nitrogen environment;

[0032] Figure 10 Normalized excitation-dependent PL spectra of H2L, solid bix (b), and dilute solution bix at room temperature;

[0033] Figure 11 FT-IR spectra of bix, H2L, and MOF-NT;

[0034] Figure 12 Fluorescence spectrum of MOF-NT emulsion after adding NACs with increasing concentration in CH3OH, λ ex = 290 nm;

[0035] Figure 13 Normalized UV-Vis spectra of some NACs and PL spectra of MOF-NT;

[0036] Figure 14 Normalized fluorescence spectra of free ligands H2L and bix in CH3OH with increasing concentration of p-nitroaniline (PNA), λ ex = 290 nm;

[0037] Figure 15 PXRD spectra of MOF-NT before and after exposure to some NACs;

[0038] Figure 16 Detection data of the fluorescence titration method for the MOF-NT emulsion containing acetone, λ ex = 290 nm;

[0039] Figure 17 are the fluorescence intensity and quenching efficiency of MOF-NT in water after adding different organic solvents and acetone successively;

[0040] Figure 18 is the fluorescence titration diagram of the free ligand H2L with a healthy ketone body content in water, λ ex = 290 nm;

[0041] Figure 19 are the PXRD spectra of MOF-NT before and after adding acetone and calculated from single crystal data;

[0042] Figure 20 is the infrared spectrum of MOF-NT before and after exposure to acetone. Detailed implementation mode

[0043] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, a high-efficiency photoluminescent material with flexible electronics and its preparation method proposed according to the present invention are described in detail below in terms of its specific implementation mode, features and effects. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0044] The first aspect of the present invention provides a high-efficiency photoluminescent material with flexible electronics, and the single crystal structure molecular formula of the material is: [Zn(μ-L)(μ-bix)] n ·0.33nH2O; wherein, H2L is biphenyl-3,5-dicarboxylic acid, bix is 1,4-bis[(1H-imidazol-1-yl)methyl]benzene, and the structural formula is as Figure 1 shown. In the material, the imidazole-containing group serves as a coordination donor and has a multiple resonance structure due to the characteristics of rapid intramolecular electron transfer; imidazole derivatives are ideal materials for preparing electronically flexible metal-organic materials. Specifically, the single crystal structure of the material is the R3c space group of the trigonal system and a three-dimensional MOF structure. More specifically, as Figure 5 shown, the asymmetric unit contains a Zn(II) center, a deprotonated H2L ligand (dep-H2L) and a μ-bix ligand. Figure 5 In (a) of Figure 5 is the coordination environment diagram around the central tetracoordinated Zn(II); Figure 5 In (b) of 5,8) of the single-node four-coordinate network. Zn1 is a four-coordinate atom with a distorted tetrahedral {ZnN2O2} coordination configuration; the coordination environment around the central four-coordinate Zn(II) is as shown in (a) of Figure 5 . The coordination environment is filled with two N atoms and two carboxylic acid O atoms; the N atoms come from the imidazole groups between the μ-bix linkers, and the O atoms come from the spacers of different dep-H2L ligands. Among them, in the dep-H2L ligand, both carboxylic acid groups adopt the terminal monodentate coordination mode; the dep-H2L and μ-bix ligands provide an interconnected bridge for the Zn1 center and its adjacent four centers, thus forming a three-dimensional tubular metal-organic framework with a benzene ring-modified one-dimensional channel; the three-dimensional MOF of the tubular cavity filled with lattice H2O molecules is as shown in (b) of Figure 5 . It should be noted that the size of the nano-tubular channel of MOF-NT extending along the crystallographic c-axis is about And from a topological consideration, the three-dimensional underlying network is composed of four-coordinate Zn1 nodes, two-coordinate μ-dep-H2L and μ-bix linkers. This single-node four-coordinate network is an unprecedented topological structure that can be represented by a point symbol (7 5 .8), as shown in (c) of Figure 5 .

[0045] The second aspect of the present invention provides a preparation method of an efficient photoluminescent material with flexible electrons, and the method includes:

[0046] S1. Preparation of the organic ligand H2L: Place 5-bromo-m-xylene and phenylboronic acid in a reaction vessel, and at the same time add potassium carbonate dissolved in a mixed solvent of ethanol, toluene and water to the reaction vessel and deoxygenate under N2 to obtain a reaction mixture; Stir and add Pd(PPh3)4 to the reaction mixture, and reflux for 22 h to 26 h under N2; Evaporate to dryness under vacuum, extract with CH2Cl2, and then dry with MgSO4; Use n-hexane as an eluent and obtain a colorless liquid by silica gel chromatography; Add KMnO4 in four portions to the suspension of the colorless liquid containing water and pyridine, and reflux for three days; After cooling to room temperature, filter, then rinse repeatedly with water, and then adjust the pH value to 2 with hydrochloric acid and dry to obtain the organic ligand H2L. Specifically, the synthesis method for preparing the organic ligand H2L is as shown in Figure 2 . Among them, anhydrous potassium carbonate provides a basic and dry reaction environment and does not participate in the reaction; Pd(PPh3)4 is used as a catalyst to improve the reaction efficiency; KMnO4 is used as a strong oxidant to oxidize the methyl group into a carboxylic acid. Under the basic and dry environment, 5-bromo-m-xylene and phenylboronic acid undergo a substitution reaction to form 3,5-dimethylbiphenyl, and then an oxidation reaction occurs to form biphenyl-3,5-dicarboxylic acid.

[0047] S2. Preparation of organic ligand bix: Reflux and heat the methanol solution containing imidazole and α,α'-dichlorop-xylene; dissolve the yellow viscous liquid after removing methanol by evaporation in an aqueous potassium carbonate solution; after standing, bix crystals are formed in the solution; and recrystallize from the solution to obtain the organic ligand bix. Specifically, the synthesis method for preparing the organic ligand bix is as Figure 3 shown, where anhydrous potassium carbonate is used as a catalyst and does not participate in the reaction, which can improve the reaction efficiency. In a basic and dry environment, imidazole and α,α'-dichlorop-xylene undergo a substitution reaction to form 1,4-bis[(1H-imidazol-1-yl)methyl]benzene.

[0048] S3. Preparation of [Zn(μ-L)(μ-bix)] n ·0.33nH2O: Place the H2O / CH3CN mixed solvent of the mixture containing the organic ligand H2L, organic ligand bix, and Zn(OAc)2·2H2O in a stainless-steel high-pressure vessel; stir and heat the mixture, and then cool it to room temperature overnight to obtain the needle-shaped crystal [Zn(μ-L)(μ-bix)] n ·0.33nH2O. Specifically, the stainless-steel high-pressure vessel is a stainless-steel autoclave lined with Teflon.

[0049] The third aspect of the present invention provides the application of the above-mentioned high-efficiency photoluminescent material with flexible electronics as a fluorescent probe in the field of monitoring nitro explosives. MOF-NT utilizes the combined characteristics of multi-component PL and ordered porosity and can be used as a highly sensitive fluorescent probe to distinguish and detect volatile organic compounds, showing a discriminatory PL response between isomers of nitroaromatic compounds; this makes it have application prospects in selectively monitoring specific types of nitro explosives.

[0050] The fourth aspect of the present invention provides the application of the above-mentioned high-efficiency photoluminescent material with flexible electronics as a sensor in the fields of toxicology and physiology.

[0051] All the drugs were purchased from chemical reagent companies and used directly without further purification.

[0052] Example 1

[0053] The single-crystal structure of a high-efficiency photoluminescent material with flexible electronics proposed by the present invention, and the molecular formula of the single-crystal structure of the complex material is: [Zn(μ-L)(μ-bix)] n ·0.33nH2O; where H2L is biphenyl-3,5-dicarboxylic acid; bix is 1,4-bis[(1H-imidazol-1-yl)methyl]benzene.

[0054] Single crystals of appropriate size were selected using a microscope. At room temperature, a Bruker APEX-II CCD single-crystal diffractometer (graphite monochromated Mo-Kα incident radiation ) was used to collect diffraction data. The intensity data were integrated using Bruker InstrumentService v4.2.2 and SAINT V8.34A software. Empirical absorption correction was carried out using the SADABS program. The structure was solved by the direct method, and the positions of non-hydrogen atoms were located from the experimental structure. The crystal data were refined by full-matrix least-squares methods, and anisotropic refinement was carried out on F 2 using the SHELXTL program package to obtain the crystallographic data.

[0055]

[0056]

[0057] Example 2

[0058] Organic ligand H2L: 5-Bromomesitylene (38.85 mmol, 7.19 g) and phenylboronic acid (46.65 mmol, 5.69 g) were placed in a 250 mL round-bottom flask. Potassium carbonate (90.13 mmol, 12.44 g) was dissolved in ethanol (45 mL) / toluene (90 mL) / H2O (45 mL), then added to the reaction mixture, and deoxygenated under N2 for 30 min. Pd(PPh3)4 (1.125 g, 0.97 mmol) was added to the reaction mixture with stirring, and the mixture was refluxed under N2 for 22 h to 26 h. The synthesized mixture was evaporated to dryness under vacuum, extracted with dichloromethane, and then dried over magnesium sulfate. The crude product was obtained by evaporating the solvent under reduced pressure. The residue was purified by silica gel column chromatography using n-hexane as the eluent to obtain a colorless liquid (yield: 6.03 g, 85.3% based on 5-bromomesitylene). Potassium permanganate (36.05 g, 228.12 mmol) was added in four portions to a suspension of the colorless liquid (6.03 g, 33.13 mmol) in water (180 mL) and pyridine (90 mL), and the mixture was refluxed for 3 days. After cooling to room temperature, the solid mixture was filtered and washed repeatedly with water. The insoluble solid was filtered off, and the filtrate was acidified to pH ~ 2 with hydrochloric acid. A white solid was obtained and dried under vacuum to obtain H2L (yield: 6.45 g, 80.4% of the colorless liquid).

[0059] Example 3

[0060] Organic ligand bix: A solution containing imidazole (3.16 g, 46.4 mmol) and α,α'-dichlorop-xylene (0.78 g, 4.46 mmol) was refluxed in methanol (50 mL) for 17 h to 19 h. The yellow viscous liquid after removing methanol by evaporation was dissolved in an aqueous potassium carbonate solution (6.13 g, 100 mL). After standing for a period of time, bix crystals were formed in this solution and further recrystallized from water.

[0061] Example 4

[0062] Complex single crystal material [Zn(μ-L)(μ-bix)] n ·0.33nH2O: A mixture of H2L (0.1 mmol, 0.0242 g), bix (0.1 mmol, 0.0238 g) and Zn(OAc)2·2H2O (0.15 mmol, 0.0329 g) in a mixed solvent of H2O / CH3CN (6 mL / 3 mL) was placed in a Teflon-lined stainless steel autoclave (25 mL). The mixture was stirred briefly and then heated at 165 °C to 175 °C under autogenous pressure for 2.9 days to 3.1 days. Then the reaction mixture was cooled to room temperature overnight, and needle-like crystals suitable for X-ray diffraction were separated with a yield of 80%.

[0063] Example 5

[0064] Fluorescence titration method: At room temperature, the fluorescence spectrum of the MOF-NT emulsion was measured in CH3OH with a typical concentration of 1.0 g / L as Figure 16 shown. Figure 16 In (a), it is the fluorescence titration method of the MOF-NT emulsion containing acetone, λ ex = 290 nm, and the fluorescence color change before and after adding acetone to water is shown in the figure; Figure 16 In (c), it is the fluorescence titration of the MOF-NT emulsion with a ketone content within the healthy range; Figure 16 In (d), it is the ratio plot of the luminescence intensities of MOF-NT and H2L against the acetone concentration; I0 and I are the PL intensities with and without acetone, respectively. According to the linear equation shown in the figure, the solid line is the best fit and the dashed line is guided by the human eye. The titration experiment was carried out by gradually adding the analyte in an incremental manner. Each data was repeated at least three times and the average value was obtained. The fluorescence quenching efficiency was obtained according to the formula (1 - I / I0)×100%, where I0 and I are the maximum intensities in the absence and presence of the analyte, respectively. The fluorescence titration method of the MOF-NT emulsion containing acetone is as Figure 16 shown in (a); the fluorescence titration of the MOF-NT emulsion with a ketone content within the healthy range is as Figure 16as shown in (c); the variation of the luminescence intensity ratio I / I0 of MOF-NT and H2L with acetone concentration is as Figure 16 shown in (d). Figure 17 In (a), it is the fluorescence intensity diagram of MOF-NT in water after adding different organic solvents and then adding acetone. The fluorescence intensity of MOF-NT in water after adding different organic solvents and then adding acetone is as Figure 17 shown in (a); the fluorescence titration of the free ligand H2L with a healthy ketone body content in water is as Figure 18 shown.

[0065] From Figure 16 in (a), it can be seen that when the acetone concentration increases to 3%, the emission intensity decreases by more than 80% and there is a slight blue shift. Therefore, MOF-NT can achieve the function of a fluorescence switch by exposing the crystal sample to acetone vapor; from Figure 16 in (c), it can be seen that according to the standards of the US Environmental Protection Agency, the detection of acetone can be carried out in ketone bodies at a healthy level; from Figure 16 in (d), it can be seen that the PL intensity of the MOF-NT emulsion is approximately proportional to the amount of acetone, which also proves the feasibility of detecting trace acetone in pure water; from Figure 18 it can be seen that the change in the PL spectrum of the free ligand H2L caused by the same concentration of acetone under the same conditions is negligible. Due to the ordered crystal channels, the MOF sensing material has significant advantages in terms of sensitivity.

[0066] Example 6

[0067] Fluorescence reversibility experiment: 20 mg of MOF-NT was exposed to acetone vapor in a closed tube, and the emission spectrum was recorded. After drying the sample in air, the emission spectrum was recorded again. After multiple cycles, MOF-NT can still exhibit reversible sensing ability, demonstrating the fluorescence regeneration ability of MOF-NT. After several cycles, the reversible change in the maximum emission intensity is as Figure 16 shown in (b), Figure 16 in (b) is the reversible change in the maximum emission intensity after several cycles. From Figure 16 in (b), it can be seen that even after multiple cycles, the fluorescence switching process is still highly reversible.

[0068] Example 7

[0069] 400 cm of the liquid nitrogen closed-cycle cryostat -1 ~4000 cm -1In the regions (w: weak, b: broad, m: medium, s: strong), infrared spectra were recorded on a Nicolet Magna-IR 750 spectrophotometer; the infrared spectra of bix, H2L, and MOF-NT are as Figure 11 shown; among which the infrared data of MOF-NT (KBr pellets, cm -1 -1): 3423(b), 3124(w), 3041(w), 2925(w), 2854(w), 1615(s), 1438(m), 1382(m), 1280(m), 1233(w), 1095(s), 1032(w), 951(w), 849(w), 790(w), 769(w), 760(s), 722(w), 687(m), 656(w), 628(w), 467(w); the infrared spectra of MOF-NT before and after exposure to acetone are as Figure 20 shown. As can be seen from Figure 20 , the characteristic peaks of MOF-NT show obvious changes in the FT-IR spectra. At 1617 cm -1 , the COOH functional group with asymmetric stretching vibration shows a slight shift to lower wavenumbers; meanwhile, new peaks of C=O and C-OH stretching vibrations appear at 1558, 1506, and 1391 cm -1 . The results indicate that there is absorption of acetone on the surface of the hydrophobic channels in MOF-NT, promoting non-emissive ways of excitation and recombination.

[0070] Example 8

[0071] Elemental analysis (C, H, N) of C 28 H 22.67 N4O 4.33 Zn was carried out using a Perkin-Elmer 2400 analyzer: Calculated values: C, 61.83; H, 4.08; N, 10.30. Experimental values: C, 61.88; H, 4.12; N, 10.38.

[0072] Example 9

[0073] PXRD measurements were carried out on a Bruker D8 Advance X-ray powder diffractometer using Cu Kα radiation . The PXRD patterns of MOF-NT before and after exposure to some NACs are as Figure 15 shown; the PXRD patterns of MOF-NT before and after adding acetone and calculated from single crystal data are as Figure 19 shown.

[0074] Figure 15 (a), Figure 15 (b) and Figure 15The NACs in (c) are MNT, ONT, PNT; MNP, ONP, PNP; MNA, ONA, PNA respectively. As can be seen from Figure 15 under the action of different NACs, the MOF-NT sample maintained high crystallinity, and the fluorescence change was not related to the framework collapse; as can be seen from Figure 19 the PXRD patterns of MOF-NT before and after exposure to acetone were exactly the same as the simulated patterns, indicating that exposure to acetone did not cause framework collapse or phase transformation.

[0075] Example 10

[0076] The fluorescence spectra were collected using an Edinburgh Model FS5 instrument; Figure 6 in (a) is the emission-dependent excitation spectrum and electronic absorption spectrum diagram at room temperature in the thin film; Figure 6 in (b) is the normalized PL spectrum diagram at the excitation wavelength of 290-470 nm, which is the emission spectrum dependent on excitation and the crystal color change diagram. In the thin film, the emission-dependent excitation spectrum of crystalline MOF-NT at room temperature is as shown in Figure 6 (a); the normalized PL spectrum at the excitation wavelength of 290-470 nm is as shown in Figure 6 (b); the PL spectra of MOF-NT in the presence of different organic solvents are as shown in the Figure 7 inset; the normalized PL spectrum of MOF-NT emulsion in methanol with gradually increasing NACs concentration is as shown in Figure 8 ; the normalized excitation-dependent PL spectra of H2L (a) in the solid state, bix (b) in the solid state and bix (c) in the dilute solution at room temperature are as shown in Figure 10 ; the fluorescence spectra of MOF-NT emulsion after adding NACs with increasing concentration in CH3OH are as shown in Figure 12 ; the normalized PL spectrum of MOF-NT is as shown in Figure 13 ; the normalized fluorescence spectra of free ligands H2L (a) and bix (b) in CH3OH when the concentration of p-nitroaniline (PNA) increases are as shown in Figure 14 .

[0077] As can be seen from Figure 6 (a), when λ em exceeds 382 nm, the excitation spectrum broadens, and the excitation light with wavelengths between 250 nm and λ em can be absorbed, and there is a broad electronic absorption band in MOF-NT. As can be seen from Figure 6As can be seen from (b), under relatively high-energy excitations, such as 290 nm and 310 nm, the PL spectrum exhibits a bimodal feature, namely a strong emission band at 343 nm and a weak broad emission band near 450 nm. When the excitation wavelength exceeds 330 nm, the emission peak shows a continuous red shift from 343 nm to 505 nm. The crystal powder photograph shows the corresponding color change from blue to yellow.

[0078] From Figure 7 it can be seen that these nitroaromatic compounds that can be identified and detected by MOF-NT include nitrobenzene (NB), o-nitroaniline (ONA), m-nitroaniline (MNA), p-nitroaniline (PNA), o-nitrophenol (ONP), m-nitrophenol (MNP), p-nitrophenol (PNP), o-nitrotoluene (ONT), m-nitrotoluene (MNT), and p-nitrotoluene (PNT), etc.; fluorescence quenching occurs in nitrobenzene (NB) in the presence of methanol and in acetone.

[0079] Among them, Figure 8 the NACs at (a), (b), and (c) are p-nitrotoluene (PNT), p-nitrophenol (PNP), and p-nitroaniline (PNA), respectively; (d) is the emission displacement response diagram of MOF-NT to different analytes; (e) is the normalized fluorescence spectrum diagram of the mechanical mixture of H2L and bix in methanol under the condition of increasing the concentration of p-nitroaniline (PNA); (f) is the schematic diagram of the multiple energy transfer process in MOF-NT induced by specific analytes; among them, bix is the ligand in the MOF, and bix * is the ligand of the mixture powder. From Figure 8 it can be seen that, first of all, in the presence of PNP, the spectrum shows an obvious red shift, while the increase of other NACs (such as NB, PNT) cannot cause an obvious emission displacement; secondly, when PNA is present in the CH3OH emulsion of MOF-NT, the low-energy emission band (LE band) of the ligand bix at 450 nm gradually changes, and with the increase of the PNA concentration, the intensity of the LE band continues to increase, while the high-energy emission (HE band) shows a small blue shift; in addition, when the mechanical mixture containing H2L and bix exists simultaneously, the energy transfer between PNA and bix is blocked, and only the energy transfer process between H2L and PNA occurs, and this phenomenon is significantly different from the continuous energy transfer process of MOF-NT (dep-H2L→PNA→bix).

[0080] Figure 10 The normalized excitation-dependent PL spectra of H2L, solid-state bix (b), and dilute solution bix at room temperature are shown at (a), (b), and (c), respectively. From Figure 10It can be seen that the excitation dependence of MOF-NT comes from the bix ligand, while the high-energy emission at 343 nm comes from the deprotonated H2L ligand and is independent of the excitation.

[0081] Figure 12 The NACs at (a) to (g) are NB, MNT, ONT, MNP, ONP, MNA, and ONA respectively. From Figure 12 It can be seen that, different from the obvious red shift of the spectrum in the presence of PNP, only slight blue shifts are produced in the presence of other isomers (such as MNP and ONP), indicating a specific reaction to nitrophenol isomers.

[0082] To further clarify the energy transfer process, the PL responses of pure ligands (such as H2L, bix, and their mixtures) in the presence of specific analytes were continued to be studied. Figure 14 The normalized fluorescence spectra of the free ligands H2L and bix in CH3OH when the concentration of p-nitroaniline (PNA) increases are shown at (a) and (b) respectively, λ ex = 290 nm. From Figure 14 It can be seen that in the CH3OH solution containing only H2L, PNA causes a new peak near 425 nm, and this peak continues to increase with the increase of the PNA concentration. Under the same conditions, in the solution containing only bix, the increase in the concentration of PNA causes the LE band at 450 nm. The results show that the energy transfer processes between H2L and PNA (H2L→PNA) and between PNA and bix (PNA→bix) are effective.

[0083] Example 11

[0084] The quantum efficiency was measured on the same instrument by a direct method using an integrating sphere (diameter 150 mm, BaSO4 coating); the variation of the PL quantum efficiency at different excitation wavelengths is as Figure 6 shown at (c), Figure 6 At (c) is the graph of the variation of the photoluminescence quantum yield at different excitation wavelengths. From Figure 6 It can be seen from (c) that MOF-NT has a tunable photoluminescence quantum yield (PLQY) at room temperature, with a maximum value of 36.7%.

[0085] Example 12

[0086] The UV-visible spectra were recorded on a METASH UV-8000 spectrophotometer using an air-free quartz cuvette (3.5 mL, path length = 1 cm). The normalized UV-visible spectra of crystalline MOF-NT at room temperature in the thin film are as Figure 6 shown at (a); the normalized UV-visible spectra of some NACs are as Figure 13 shown.

[0087] From Figure 6 It can be seen that although the absorption tail is quite extensive, it exhibits the characteristics of a relatively wide electronic transition band; from Figure 13 it can be seen that there is a substantial overlap between the absorption spectra of PNP or PNA and the emission spectrum of MOF-NT, which can make the resonance energy transfer from the high-energy emissive fluorophore (dep-H2L) to the non-emissive NACs more smooth.

[0088] Example 13

[0089] Thermogravimetric analysis: The thermogravimetric plot of MOF-NT in a nitrogen environment is as Figure 9 shown.

[0090] Example 14

[0091] The PL lifetime was recorded using a single-photon counting (TCSPC) spectrometer and an Edinburgh FLS980 steady-state fluorometer with a pulsed xenon lamp as the excitation source. The excitation-related excited-state lifetime curves monitored at different emission maxima are as Figure 6 shown in (d) of Figure 6 where (d) in Figure 6 is the excitation-related excited-state lifetime curve monitored at different emission maxima. It can be seen from (d) in

[0092]

[0093] Example 15

[0094] As Figure 12 shown, the concentrations of different NAC analytes when significant and complete quenching occurs in the presence of a MOF-NT.

[0095]

[0096] Note: At 298K, a MOF-NT in MeOH (1 mg / mL, 2 mL). Nitrobenzene (NB), o-nitroaniline (ONA), m-nitroaniline (MNA), p-nitroaniline (PNA), o-nitrophenol (ONP), m-nitrophenol (MNP), p-nitrophenol (PNP), o-nitrotoluene (ONT), m-nitrotoluene (MNT), p-nitrotoluene (PNT). The quenching rate (%) of the MOF-NT emulsion in methanol after adding different volatile organic compounds (3%) is as Figure 17 shown in (a) of Figure 17As shown in (b) in Figure 17 As can be seen from (b) in , in the presence of other interfering compounds, no significant change in the quenching efficiency was observed, indicating the high selectivity of MOF-NT as a luminescent probe for detecting acetone.

[0097] Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. An efficient photoluminescent material with flexible electronics, characterized in that, The structural molecular formula of the said material is: [Zn(μ-L)(μ-bix)] n ·0.33nH2O; Among them, L is the deprotonated form of biphenyl-3,5-dicarboxylic acid, and bix is 1,4-bis[(1H-imidazol-1-yl)methyl]benzene; The material belongs to the trigonal crystal system and the R3c space group. The smallest asymmetric unit contains one Zn(II) center, one deprotonated H2L ligand (dep-H2L), and one μ-bix ligand each; Zn1 has four coordination atoms and adopts a {ZnN2O2} distorted tetrahedral coordination configuration. The N atoms come from the imidazole groups between the μ-bix linkers, and the O atoms come from the spacers of different dep-H2L ligands; Among them, in the dep-H2L ligand, both carboxylic acid groups adopt a terminal monodentate coordination mode; the dep-H2L and μ-bix ligands provide an interconnected bridge for Zn1 and its adjacent four centers, thus forming a three-dimensional tubular metal-organic framework with benzene ring-modified one-dimensional channels; From a topological perspective, the three-dimensional underlying network is composed of four-coordinated Zn1 nodes, two-coordinated μ-dep-H2L, and μ-bix linkers. The single-node four-coordinated network is a topological structure represented by the point symbol (7 5 .8).

2. The high-efficiency photoluminescent material with flexible electronics according to claim 1, characterized in that, The emission peak position of the material is shifted by at least 170 nm.

3. The high-efficiency photoluminescent material with flexible electronics according to claim 1, characterized in that, At the optimal excitation wavelength, the photoluminescence quantum yield of the material at room temperature can reach up to 36.7%.

4. The preparation method of the high-efficiency photoluminescent material with flexible electronics according to any one of claims 1 to 3, characterized in that, The method includes: S1. Preparation of the organic ligand H2L: Place 5-bromo-m-xylene and phenylboronic acid in a reaction vessel, and at the same time add potassium carbonate dissolved in a mixed solvent of ethanol, toluene, and water to the reaction vessel and deoxygenate under N2 to obtain a reaction mixture; Stir and add Pd(PPh3)4 to the reaction mixture, and reflux for 22 h to 26 h under N2; Evaporate to dryness under vacuum, extract with CH2Cl2, and then dry with MgSO4; Use n-hexane as the eluent and obtain a colorless liquid by silica gel chromatography; Add KMnO4 in four portions to the suspension of the colorless liquid containing water and pyridine, and reflux for three days; Filter after cooling to room temperature, then rinse repeatedly with water, and then adjust the pH value to 2 with hydrochloric acid and dry to obtain the organic ligand H2L; S2. Preparation of the organic ligand bix: Carry out reflux heating treatment on a methanol solution containing imidazole and α,α'-dichloro-p-xylene; Dissolve the yellow viscous liquid after evaporating methanol in an aqueous potassium carbonate solution; After standing, bix crystals are formed in the solution; And recrystallize from the solution to obtain the organic ligand bix; S3. Preparation of [Zn(μ-L)(μ-bix)] n ·0.33nH2O: Place the H2O / CH3CN mixed solution of the mixture containing the organic ligand H2L, the organic ligand bix, and Zn(OAc)2·2H2O in a stainless steel high-pressure vessel; stir and heat the mixture, and then cool it to room temperature overnight to obtain the material [Zn(μ-L)(μ-bix)] in the form of needle crystals n ·0.33nH2O; In the step S3, the molar ratio of the organic ligand H2L, the organic ligand bix, and Zn(OAc)2·2H2O is (1.9 - 2.1):(1.9 - 2.1):(2.9 - 3.1); The volume ratio of H2O to CH3CN in the H2O / CH3CN mixed solvent is (1.8 - 2.2):(0.9 - 1.1); In the step S3, the reaction temperature for heating the stirred mixture is 165 °C to 175 °C, and the reaction time is (2.9 - 3.1) days.

5. The preparation method of the high-efficiency photoluminescent material with flexible electronics according to claim 4, characterized in that, In the step S1, the molar ratio of 5-bromo-m-xylene, phenylboronic acid, and potassium carbonate is (38.75 - 38.95):(46.55 - 46.75):(89.93 - 90.33); The molar ratio of the Pd(PPh3)4 to potassium permanganate is (0.87 to 1.07):(227.82 to 228.42); The volume ratio of ethanol, toluene and water in the mixed solvent is (0.9 to 1.1):(1.9 to 2.1):(0.9 to 1.1); The volume ratio of water to pyridine in the suspension is (1.9 to 2.1):(0.9 to 1.1).

6. The preparation method of the high-efficiency photoluminescent material with flexible electronics according to claim 4, characterized in that, In the step S2, the molar ratio of the imidazole to α,α'-dichloroxylene is (46.2 to 46.6):(4.36 to 4.56); The volume ratio of the methanol to the aqueous potassium carbonate solution is (0.9 to 1.1):(1.9 to 2.1); The concentration of the aqueous potassium carbonate solution is 61.3 g / L.

7. The preparation method of the high-efficiency photoluminescent material with flexible electronics according to claim 4, characterized in that, In the step S2, the time of the reflux heating treatment is 17 h to 19 h.

8. Use of the high-efficiency photoluminescent material with flexible electronics as claimed in any one of claims 1 to 3 as a fluorescence probe in the field of monitoring nitro explosives.

9. Use of the high-efficiency photoluminescent material with flexible electronics as claimed in any one of claims 1 to 3 as a sensor in the fields of toxicology and physiology.

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